1. Field
The present invention relates generally to wireless communications, and more specifically, to the selective processing of a downlink common control channel.
2. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for remote subscribers. As used herein, the term “cellular” system encompasses systems using either cellular or personal communications services (PCS) frequencies. Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS95). IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems are promulgated by the Telecommunication Industry Association (TIA) and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and incorporated by reference herein. An exemplary system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in the draft versions of IS-2000 and has been approved by the TIA. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.
Transmissions between component parts of a WCDMA system can be sent in a time division duplex mode (TDD) or a frequency division duplex mode (FDD), in accordance with the frequency bands available to a service provider. Due to the complexity of permitting operations in either mode, the system transmits information in accordance with logical channels and physical channels. Data is encoded and interleaved according to the logical channel to which the data is assigned, and the logical channels are then mapped onto physical channels. The number and types of logical channels and physical channels vary depending upon the direction the signal is being sent. Transmissions from the remote station (also known as a mobile station) to the base station are referred to as the “uplink” and the transmissions from the base station to the remote station are referred to as the “downlink.”
On the downlink, the logical channels are classified as control channels or traffic channels. Control channels are the Broadcast Control Channel (BCCH), Paging Control Channel (PCCH), Dedicated Control Channel (DCCH), Common Control Channel (CCCH), and the Shared Channel Control Channel (SHCCH). Traffic channels are the Dedicated Traffic Channel (DTCH) and the Common Traffic Channel (CTCH).
The embodiments described below are directed towards the selective processing of the CCCH by a remote station. Presently, a WCDMA system is designed so that the CCCH is common amongst all remote stations operating within the range of a serving base station, provided that the remote stations have been assigned common transport channels in uplink and in downlink. Hence, all remote stations that are using uplink and downlink common transport channels must demodulate and decode all messages on the CCCH. If a message is not specifically targeted towards a remote station, then the remote station must discard the message. For example, if the serving base station transmits 100 individual messages to 100 individual remote stations on the CCCH, then each remote station would demodulate and decode all 100 messages, of which 99 irrelevant messages would be discarded as being targeted for another.
The above requirement to demodulate and decode all messages on the CCCH is wasteful of processing resources, but the requirement is implemented in order to solve the problem of providing update information to a remote station. The CCCH is used to exchange signaling information when the DCCH is not available, which occurs after a cell reselection, for example. Messages on the CCCH typically comprise update information that will allow a remote station to continue processing targeted messages received on the DCCH and allow the allocation of dedicated transport channels to the remote station.
The embodiments that are described herein are for reducing the need of a remote station to demodulate and decode all messages on the CCCH, so that the amount of processing resources required to successfully decode the CCCH is reduced. The CCCH is successfully decoded if a remote station can determine information specifically targeted to itself on the CCCH. If the remote station need not demodulate and decode all irrelevant CCCH messages, then a corresponding savings in power consumption is produced, which is beneficial to the battery life of the remote station.